The present invention relates to a method and to apparatus for monitoring and controlling the filling of receptacles which are successively engaged in a production line filling installation.
In many industries, such as the food, the chemicals, the oil, and the pharmaceuticals industries, there is a need to package materials which are more or less fluid for subsequent distribution. To be profitable, the packaging operation must be both fast and accurate. Modern installations are fast, but there is still a need to improve accuracy. Ideally, each receptacle would be filled with exactly the desired quantity of material. However, achieving such accuracy runs into several problems which are due in particular to the fast throughput required by the filling installations and also to the physical properties of the materials being packaged. Fast throughput makes it difficult to verify the quantity of material which is effectively inserted into each receptacle, while the key physical properties of the materials to be packaged, even when such materials are homogeneous, are their density and their viscosity, both of which are liable to vary with temperature and thus have an effect on the quantities actually dispensed. If receptacles moving along a production line filling installation are to be accurately filled, it is necessary not only to dispense an exact quantity of the material to be packaged but also to verify that the receptacles (either individually or statistically) contain only the desired exact quantity so as to be able, if necessary, to correct the dispensing of material to subsequent receptacles.
One known way of dispensing material to receptacles is to use a volumetric dispenser e.g. of the type including timer means controlling the opening and closing of an orifice from a tank of the material to be packaged, or else of the type comprising a piston and cylinder assembly in which the stroke of the piston defines the volume of the material to be dispensed. Such dispensers are adjusted to dispense a volume of a given material at a given temperature. If the temperature of the material inserted therein varies over the course of a working day, or over the course of several days, etc., the quantity of material actually dispensed to the receptacles will vary. In order to verify the quantity of material inserted in the receptacles, and if necessary to modify the adjustment of the dispensers so as to compensate for any underfill or overfill, it is known to use a balance since weight is the only characteristic which can be used to accurately define the quantity of a material regardless of its temperature.
U.S. Pat. No. 2,925,835 describes a method and apparatus for monitoring and controlling the filling of receptacles which are successively engaged in a production line filling installation. In the example described in that U.S. patent, the receptacles are conveyed by a moving belt to a single filling station where they are filled one-by-one with a quantity of material which is dispensed by a volumetric dispenser including a timer. Once filled, the receptacles continue their path along the moving belt until they arrive at a point where they are removed mechanically from the moving belt one after the other and placed on a fixed balance located adjacent to the belt. They are weighed thereon, and then mechanically replaced on the belt. The weight of the full receptacle is compared with a set value, and if necessary, the adjustment of the volumetric dispenser is modified. Although such a system is theoretically capable of solving the problems encountered, it nevertheless suffers from several drawbacks in practice: firstly transferring a receptacle from the moving belt to a balance, waiting a suitable length of time for the balance to settle, and then transferring the receptacle back to the belt limits the possible throughput to a fairly low value; and secondly the system makes no allowance for receptacles of different tare weights, even though mass produced receptacles, eg. made of glass, can often vary considerably in their empty or tare weights. It can thus impossible to determine the weight of a packaged material with sufficient accuracy.